2. Brief History Of Genetics

• Diagram A

3. Current Applications Of Genetic Engineering

• Plants
• Livestock
• Human Genome Project and Disease Control

4. Cloning Techniques A - Cells

• Definition of Main Terms
• Plasmid Cloning and the Polymerase Chain Reaction
• Diagram A
• Diagram B
• Java Diagram and sound

5. Cloning Techniques B - Animals

• Gurdon’s Trials with Tadpoles
• Cycling Cells
• Roslin’s ReCreation: Connecting the Cell Cycle to Cloning
• Dolly’s Development
• Diagram A
• Diagram B
• Diagram A - With Sound
• Diagram B - With Sound

John Gurdon, with the aid of a good microscope and some thin needles, "sucked" the nucleus out of a frog oocyte. This "empty" oocyte is called an enucleated oocyte. An enucleated oocyte can not differentiate or become a zygote.

It became more interesting when Gurdon took a nucleus out of a frog’s gut cell, and put it into an enucleated oocyte. This process of creating a "new" cell by changing the nucleus is called nuclear transfer. He repeated this process so that he had many new cells with identical genetic material. Most of these cloned cells began behaving like zygotes, with cells dividing and differentiating until they became tadpoles.

By making tadpoles from adult cells, Gurdon proved that differentiation was reversible, something that scientists had previously argued about and discredited.

However, the experiment was not a complete success. All the tadpoles died before they became frogs. The experiment was repeated by other scientists, but none of the tadpoles reached adulthood. Even today this remains unexplainable.

But that wasn’t the only problem. Nuclear transfer only worked for frogs! Scientists decided that differentiation just wasn’t reversible in mammals.